Association between long-term exposure to ambient NO₂ and prevalence of chronic kidney disease: Findings from China National Survey of Chronic Kidney Disease

Background Several studies indicate that long-term exposure to fine particulate matter (PM_2.5) may increase the risk of chronic kidney disease (CKD), but investigations on nitrogen dioxide (NO₂) are still limited.

Objective This study aims to explore the association between long-term exposure to ambient NO₂ and CKD risk in Chinese adults.

Methods Based on the health data derived from the China National Survey of Chronic Kidney Disease (CNSCKD) from January 2007 to October 2010, this study collected and matched the environmental exposure data. A generalized additive model was used to explore the association between long-term exposure to ambient NO₂ and the risk of CKD among adult residents in China. Subgroup analyses were conducted based on data stratified by gender, age, body mass index (BMI), education level, individual income per month, residence in rural or urban areas, smoking, alcohol drinking, and history of hypertension, diabetes, or myocardial infarction/stroke. Two-pollutant sensitivity analyses were used to examine the robustness of the above results.

Results A total of 47 204 subjects from 13 provinces (autonomous regions/municipalities) in China were included in this study. Longterm exposure to ambient NO₂ was positively associated with an increased risk of CKD in China, and the strongest estimated effect was found at the 5-year moving average. With a 10 μg·m^-3 increase in the 5-year moving average of NO₂, the odds ratio (OR) of CKD was 1.15 (95% CI: 1.11-1.19). The results of subgroup analyses indicated that the risk of CKD was more strongly associated with long-term NO₂ exposure in males, those 65 years and older, overweight or obese, with a diploma above junior high school, with an individual monthly income less than 500 yuan, living in rural areas, daily smokers, occasional or frequent drinkers, and without a history of hypertension, diabetes, or myocardial infarction/stroke. For instance, the estimated OR associated with an increase of 10 μg·m^-3 in NO₂ in males was 1.30 (95% CI: 1.24-1.37), which was higher than the OR=1.04 (95% CI: 1.00-1.09) in females (P for interaction < 0.01); the OR in rural populations was 1.57 (95% CI: 1.33-1.85), higher than the OR=1.09 (95%CI: 0.99-1.21) in urban populations (P for interaction < 0.01); the OR in non-diabetic adults was 1.21 (95%CI: 1.16-1.26), higher than the OR=1.01 (95%CI: 0.95-1.07) in diabetic adults (P for interaction < 0.01). The sensitivity analysis results showed that the association between long-term exposure to NO₂ and CKD risk remained robust after controlling for the confounding effect of PM_2.5 at the same exposure time window.

Conclusion Long-term exposure to ambient NO₂ is associated with an increased risk of CKD in Chinese adults. Males, residents ≥65 years, overweight or obese adults, those with an education above junior high school, those with an individual monthly income less than 500 yuan, rural residents, daily smokers, occasional or frequent drinkers, and those without a history of hypertension, diabetes, or myocardial infarction/stroke are more susceptible to the adverse kidney effects of long-term exposure to ambient NO₂.